Automatic draw bar mechanisms for removably securing machine tools within the spindles of milling machines, lathes, boring mills and the like are well known in the art. Prior art devices may be divided into nonrotating types in which the tool holder and the draw bar do not rotate with respect to each other during securing and ejecting operations and rotating types which do. Presently known nonrotating types require extensive modification of standard spindles of the machine so that the entire spindle must be replaced. In addition, special adaptors must be provided for each machine tool holder. Representative of these nonrotating types of draw bars are U.S. Pat. Nos. 3,177,775 and 3,242,819.
Rotating types of power draw bars, on the other hand, either require an expensive hydraulic motor or an electric motor with a complicated drive mechanism. Such power draw bars are disclosed in U.S. Pat. Nos. 3,027,812 and 3,374,711 and others.
Accordingly, it is an object of the present invention to provide a power draw bar which is readily adapted to standard milling machine spindles and the like.
Another object of the present invention is to provide a power draw bar which engages the normal internal threaded structure of standard tool holders without need for tool holder modification.
A further object of the present invention is to improve the useful life of both the tool holder and the draw bar over many cycles of engagement and ejection of tool holders.
An object of the present invention is to improve the safety of power draw bars by limiting the longitudinal traverse of the mechanism.